This invention relates to integrated Schottky logic (ISL) semiconductor circuits, and more particularly to an improved form of structure fabricated by triple diffusion.
In Electronics, pages 44-42, June 8, 1978 and in IEEE Journal of Solid State Circuits, Vol. SC-14, No. 3, pages 585-590, June 1979, there is described a new type of LSI logic known as ISL, an abbreviation for integrated Schottky logic. Briefly, an ISL gate comprises the combination of a current source, a normally operated, i.e. collector down, vertical npn switching transistor merged with a pnp transistor and a set of Schottky output diodes. The pnp transistor, which may have a lateral component in addition to a vertical component, clamps the npn transistor so as to prevent it from going too deeply into saturation.
Heretofore, all proposals for an ISL structure have utilized an epitaxial layer in which the components of the logic are combined. One disadvantage of the epitaxial layer form of structure is that the thickness of the epitaxial layer is a limiting factor in minimizing the base width, or thickness, of the pnp clamping transistor. The base width, in turn, limits the current gain .beta..sub.f of the pnp clamping transistor and thereby has a limiting effect on the switching speed of the npn transistor.